Gellan gum is an extracellular polysaccharide produced by the bacteria Sphingomonas elodea. Gellan gum produced by S. elodea is commercially available as Kelcogel LT100® from CP Kelco, San Diego, Calif. Commercially, gellan gum is formed by aerobic fermentation. Upon completion of fermentation, the broth is pasteurized to kill viable cells prior to recovery of the gum from the fermentation broth.
Gellan gum comprises the sugars glucose, glucuronic acid, and rhamnose in a 2:1:1 molar ratio, which are linked to form a tetrasaccharide repeat unit. Native gellan gum is acetylated and glycerylated on the same glucose residues. On average, there is one acetyl group and one half glyceryl group per tetrasaccharide repeat unit.
The method of recovery of the gellan gum affects the characteristics of the gum. Direct recovery yields a soft, flexible gel. Gellan gum has long been used in cultured, retorted, and frozen dairy products due to its textural and rheological properties. However, an off-flavor and odor develop in otherwise shelf-stable, milk-based, gellan-containing products; this flavor and odor render the foods unpalatable. The off-flavor and odor have been linked to the formation of para-cresol from substrates in milk, e.g., para-cresyl sulfate and para-cresyl glucouronide. Para-cresol is detectable in milk-based, gellan-containing products that have been treated at ultra high temperatures and stored at room temperature.
In an effort to eliminate this problem, gellan has been deacylated with hot alkali treatment. While effective in eliminating the para-cresol, the deacylation processing makes the gellan gum more brittle and less useful for certain food applications. Another approach to eliminate this problem is the pre-treatment of native gellan gum with a denaturing agent, such as sodium hypochlorite or potassium hydroxide. This approach adds material and processing costs. There is a need in the art for a gellan product which does not produce para-cresol upon prolonged storage in a sterilized dairy product and which does not require extra processing steps.